1. Field of the Invention
The present invention relates to a method for selecting gears and a gear selection device for vehicles including a first driving shaft equipped with at least two plates and a second driven shaft equipped with at least two pinions, especially for bicycles.
2. Background Information
An application of the gear variation device for a bicycle is now described. This gear selection device is of special interest for bicycles as described hereafter but it may be adapted to a large number of transmissions.
In the case of bicycles, the crank gear is equipped on its driving shaft with plates having different outer diameters and thus numbers of different teeth in ratios given according to the applications. For the purpose of simplification, a crank gear is selected with two plates or sprocket wheels A and B, the plate B having a number of teeth greater than that of the plate A and thus a larger diameter. The plate A is lower, that is, on the side of the frame and the plate is external, that is, furthest from the frame.
For each crank gear rotation, it is possible to increase the gear by moving from the plate A to the plate B.
The force to be provided increases as the crank arm difference between the distance from the pedal, where the force is exerted, to the periphery of the plate bearing the teeth, reduces.
The rear main wheel is integral, generally with the insertion of a free wheel, with a driven shaft equipped with pinions roughly aligned with the plates having different diameters and thus different numbers of teeth in ratios given according to the applications and in particular calculated according to the plates so as to obtain the desired results concerning actuation of the wheel.
In fact, the more the diameter and thus the more the number of teeth is reduced, the more is the number of wheel rotations for a given plate. The distance covered by the bicycle increases when the diameter and number of teeth reduce, which is the opposite effect with the plates.
On the other hand, the force to be supplied is much greater with a small pinion as the crank arm in question of the periphery of the pinion at the wheel spin axis reduces.
The largest gear corresponding to the largest plate and the smallest pinion needs the largest force and the smallest gear corresponding to the smallest plate and the largest pinion needs the weakest force from the user.
For the continuation of the explanations in the preamble, it is considered that the second driven shaft is also equipped with only two pinions 1 and 2, the pinion having a diameter and a number of teeth greater than those of the pinion 2.
Traditionally, there is a single chain between the plates and pinions, front gearshift means able to move the chain from one plate to another plate and rear gearshift means able to move the chain from one pinion to the other pinion.
Advantageously and traditionally, the plate 1 with the smallest diameter and the pinion 1 with the largest diameter is also internal. This has the effect of having a chain almost parallel to the traction direction for the smallest gear A/1 requiring the weakest force and for the largest gear B/2 requiring the strongest force, as explained earlier.
The two intermediate gears A/2 and B/1 are selected so that A/2 is smaller than B/1.
It is also necessary to mention that for these two intermediate gears, there is moreover a loss due to the fact that the traction of the chain is out of alignment.
Most of the systems of the prior art propose front gearshift means maneuvered by a plate control, and rear gearshift means maneuvered by a pinion control, these two controls being independent of each other.
Known gearshift means have the same design (ductile parallelogram), namely for the front a chain guide forming a yoke which moves along an axis approximately parallel to the axis of the crank gear which pushes the chain onto its taut strand provoking a controlled gear shift, and for the rear at least one small wheel moving laterally which pushes the chain into its slack strand.
The controls are of different types and many improvements have been made, especially to facilitate selection maneuvering.
The latest control, known in the trade as GRIP SHIFT makes it possible, by means of a rotary left handle and a rotary right handle, to conventionally and individually control the gearshift means of the plates and pinions respectively.
The advantage for the user is to change "speed" by maneuvering the handles and thus the chain between the various plates and pinions without letting go of the handlebar too much, which is a considerable advantage.
Nevertheless, as all users have been able to see, the physical effort required to "control" a cycle equipped with several plates and pinions is far from easy.
First of all, it is essential to assimilate the inversion of the forces between the plates and the pinions. The more the diameter of the plate increases, the more the speed increases for an identical pedalling rate, and conversely the more the diameter of the pinion increases, the more the speed reduces, again for an identical pedalling rate.
Furthermore, controls by conventional levers and rotating handles, such as the GRIP SHIFT control, are rotational and it is necessary to make the relation between the directions of rotation of the movements of these controls and the effects obtained.
It is to be noted that the losses due to the misalignment of the chain quickly become appreciable, without counting all the subsequent disagreeable effects this involves, especially noise, vibrations and ill-timed gear shifts.
Of course, these effects are even more noticeable by the user who rides occasionally. Nevertheless, competing riders are also highly affected by these effects. The cycles used are extremely sophisticated and certain cycles, such as cross-country bicycles, may include up to three plates and eight pinions, namely 24 combinations. The competing rider is then subjected during a competition to wasteful mental gymnastics seeking to select the correct plate/pinion pairing and a better alignment of the chain instead of being solely preoccupied with the course, his opponents in the race and being concerned with his race tactics. Moreover, the chain is particularly long and the rear gearshift means, the chain adjuster, have a particularly long and vulnerable yoke so as to be able to satisfy the significant free chain length variations.
Selection problems arise, especially when it is essential to quickly consider extremely different plate/pinion pairing solutions, especially when the competitor arrives at the foot of a steep incline following a rolling portion of the course, or conversely after moving from a high point when the course had a precipitous downhill incline.
Usually, these choices are not fully adapted and a bad change requires correction with at least one additional gear shift, which constitutes a loss of time, energy, and concentration which happens to even the most experienced riders.
During a car race, a maximum of six speeds is provided and numerous driving aids facilitate the various movements to enable the driver to concentrate on the race track, the approach speeds and brakings. Thus, one can readily understand the advantage of being able to simplify the approach commonly known as "change of speeds", which for bicycles is in fact a change of plates and gears.
Another specific category concerns children who also ought to benefit from a simpler mechanism so as to be able to use the benefits of gearshift means. This could increase sales and the use of a bicycle, especially with the youngest riders.
Undoubtedly, it is essential to carry out an analysis on the basis of the various choices concerning multiple combination systems, and FIGS. 1A, 1B and 1C show three tables in which the gears are indicated, as well as the displacement speeds obtained for a wheel, diameter 0.665 m, at the rate of 1 crank gear revolution per second.
Table 1A corresponds to a disposition of 3 plates and 6 pinions.
Table 1B corresponds to a disposition of 3 plates and 7 pinions.
Table 1C corresponds to a disposition of 3 plates and 8 pinions.
It shall be observed first of all that some combinations give identical or almost identical gears and thus identical or almost identical speeds, for example:
Table 1A: A4/B2 or A5/B3 or A4/C1
Table 1B: A5/C2 or A6/B4 or A7/B5
Table 1C: A4/C1 or B7/C5 or B8/C6
This clearly shows that there are identical or almost identical gears for a given item of equipment and, thus, result in redundancies.
The interest of the user, from child to competitive rider, is to make use solely of relevant gears by rejecting gears which are too similar and those which are useless, even idle gears, while retaining the best chain alignment.
It is further also essential, especially for a competitive rider, to authorize a multiple selection concerning small gears when the course has a large number of steep undulations or a multiple choice concerning large gears if the course is smooth, or even with a first set of choices concerning large gears and a second set of choices concerning small gears without any intermediate gear for long up and down climbs.
Also, from about twenty of the possible plate/pinion combinations, it is essential to retain about ten combinations with gears being progressively selected so as to cover all user requirements, these selected gears being the only ones observing a good chain alignment.
The invention therefore concerns a method for selecting progressive gear ratios from a set of gears provided by a pinion/plate pairing, as well as a device for selecting the associated gears.
To this effect, the invention concerns a method for selecting the gears of a transmission, especially of a bicycle including a train of driving plates and a train of driven pinions connected by a chain, wherein a set of plate/pinion pairs is selected having increasing or decreasing gear ratio from the set of possible plate/pinion combinations, thus suppressing the redundant ones.
It is preferable to select gears regularly stepped between the smallest gear ratio and the largest gear ratio or grouped gears according to the slopes, user and the terrain.
Again, from a double-entry table including pinions in lines and plates in columns or conversely, it is preferable to select a set of pairings per passage of one gear to the next one or preceding one by moving from one box of the table to the adjacent line box, adjacent column box or even diagonally to the adjacent box.
As regards the device, WO 91/15393 discloses a device intended to simultaneously control the front gearshift means of the plates and the rear gearshift means of the pinions so as to retain the best possible alignment of the chain between the plates and the pinions.
Also, the device is able to change the plate as soon as the chain falls or rises on the pinions so as to keep the correct alignment.
With this aim in mind, a fixed part is secured to the frame of the bicycle with a first translation immobile spin axis and bearing a stop in the form of a freely rotating roller. A casing is mounted sliding on the fixed part.
The following are provided integral with the casing:
a cam in support on the roller and driven in rotation by a set of gear reduction pinions, the movements being controlled by independent traction cables with one working in one direction and the other in an opposing direction. PA1 a cylinder for winding/unwinding the two control cables of the front gearshift means and the rear gearshift means. PA1 1 to 4 pinions with the first plate, PA1 strictly 4 pinions with the second plate, PA1 1 to 4 pinions with the third plate.
The cam has a profile so that its radius increases every 90.degree. by a constant value. Holes on the surface of the cam receive balls pressed by springs so as to provide a hard point on each rotation of 90.degree..
Functioning is thus made upon rotations of the cam, the casing moves further away or moves closer by sliding on the fixed part which ensures the traction or drawing closer of the cables at the same time as any winding of these cables with the result that via the combined addition or removal of these movements, it is possible to control the movement of the front and rear gearshift means according to a fully fixed pre-established combination.
In fact, it shall be observed that the cam needs to make a complete turn on each occasion. So as to restart a new cycle, for example if the cam has a division into four sectors of 90.degree., it is possible to carry out combinations of:
In fact, it is strictly essential to make the cam rotate by 360.degree. for the intermediate plate, which limits the choice of plate/pinion combinations.
Thus, it is not possible to select the gears but only allows a possibility of continuously retaining a good alignment of the chain.
Also, a case able to move on a fixed part on the frame is not adapted to bicycles and even less so to the cross-country bicycle sector, as mud, water, leaves and/or dust could impede the proper functioning of this casing.
Moreover, it is essential to have two cables for controlling the casing and cables for controlling the gearshift means as it is still vital to exert a traction to maneuver the casing in either direction as a recall element of reasonable size would be sufficient and in all cases would render the control even more difficult for the user to handle.
The rigidity of the device as described is evident at the moment of directly changing from the smallest diameter of the cam to the largest diameter. In fact, as regards the first direction of rotation, the elongation of the diameter is effected gradually by increasing from a constant value but in the opposite direction and there is an extremely hard passage point of 3 values.
It is also to be noted that the pinions and spindles are fragile and there is a large amount of friction. In this respect, it is to be noted that the device can only function with adjustment members (not described), but which would render the device even more delicate, both as regards mechanical resistance and adjustments and maintenance.
Reliability is naturally reduced by the significant number of mobile parts used, which also increases the cost of producing such a device.
A variant of this device is able to control a mobile casing by an endless screw driving an internally threaded cam so as to cooperate with said screw and fitted on its outer surface with throats for guiding the control cable heads of the front and rear gearshift means.
This variant is able to dispense with intermediate control cables but with one major drawback: the user has to rotate the handle by more than one turn up to three turns, which is not foreseeable in practice.
The problem of carrying out at least one complete turn during the cycle still exits, which limits the choice of combinations.
The device also prohibits any shunt of a set of combinations to revert much quicker to a given plate/pinion combination. The user must then move through all the combinations of speeds on climbing and going downhill.
In all cases, it is possible to quickly modify the pre-established combinations, which is moreover pointless in the device of this document since the only aim is to eliminate the combinations during use when the chain is not aligned, or for a pre-established choice of plates and pinions, the correct alignments and tolerances are fully known.
WO 95/03208 also describes a modified front gearshift means.
In fact, a gear shift is still effected by elastic recall means in the direction of the largest pinion or plate towards the smallest and by a manual maneuver carried out by the user in the opposite direction as the force required is greater.
Moreover, the diameter of the plates shall increase from inside to outside and conversely for the pinions so that the smallest gear and the largest gear have the best possible chain alignment.
In WO 95/03208, the elastic recall means seek to move the control yoke of the smallest plate towards the largest one. In this case, the two springs of the front and rear gearshift means work in the same direction from inside to outside.
It is to be noted that the recall spring needs to be extremely powerful as it is necessary on the plate with the largest diameter to bring the chain above the teeth so that it is then positioned on the teeth. Also, in addition to the forces to press the chain in lateral translation, that is onto the taut strand, it is necessary to bring the chain to a diameter larger than the diameter of the largest plate.
This results in an extremely difficult maneuver at the control member which requires that the user expend a large effort.
This considerable force is constant completely along the kinematics chain and all the other members accordingly need to be dimensioned, especially the cam, guiding snug and lever.
It is to be noted that the snug integral with the lever in support on the cam is pressed by the cable and by the recall force of the recall means of the gearshift means, but there is no possibility of pulling on the cable and pushing as proposed by the present invention.
In addition, if the plate/pinion pairings are taken into account, the chain alignment is not an observed parameter. Table II of FIG. 8 of WO 95/03208 shows a combination of the plate B with the smallest pinion, which is not a desirable combination.